Megapleonum wangjiani, Huang & Shih & Ahyong, 2025

Huang, Chao, Shih, Hsi-Te & Ahyong, Shane T., 2025, Four new freshwater crab species of the genus Megapleonum Huang, Shih & Ahyong, 2018 (Crustacea, Decapoda, Potamidae) from Guangdong, China, ZooKeys 1244, pp. 1-27 : 1-27

publication ID	https://doi.org/10.3897/zookeys.1244.148112
publication LSID	lsid:zoobank.org:pub:CCCA8237-6587-44BD-A25E-41BD00928A11
DOI	https://doi.org/10.5281/zenodo.15791872
persistent identifier	https://treatment.plazi.org/id/C80D0340-D964-5FCD-8913-422A01FB4647
treatment provided by	ZooKeys by Pensoft
scientific name	Megapleonum wangjiani
status	sp. nov.

Treatment

Megapleonum wangjiani sp. nov.

Figs 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7 , 11 A, B View Figure 11 , 13 B, C View Figure 13

Type material.

Holotype: • SYSBM 002144 , male (11.7 × 9.7 mm), Datianding , Dawuling Nature Reserve, Maoming City, Guangdong Province, China, 22.29°N, 111.22°E, under rocks in small seepage, coll. Chao Huang, November 2018 GoogleMaps . Paratypes: • SYSBM 002145 –002147, 3 males (11.6 × 9.5 mm, 10.9 × 9.0 mm, 8.3 × 6.9 mm), same data as holotype. SYSBM 002148 –002151, 4 females (16.7 × 12.8 mm, 15.0 × 11.3 mm, 14.6 × 11.4 mm, 9.3 × 7.5 mm), same data as holotype GoogleMaps . • NNU 16 C-201811 MW , 1 male (10.3 × 8.3 mm), 1 female (14.6 × 11.4 mm), same data as holotype GoogleMaps .

Diagnosis.

Carapace broader than long; dorsal surface slightly convex, postorbital, epigastric cristae weak, rugose, almost confluent (Fig. 5 View Figure 5 ). Maxilliped 3 merus width ~ 1.2 × length; ischium width ~ 0.7 × length; exopod reaching slightly beyond anterior edge of ischium, without flagellum (Fig. 7 A View Figure 7 ). Ambulatory legs with dense setae; pereiopod dactylus shorter than propodus (Fig. 7 View Figure 7 ). Male anterior thoracic sternum very broad, width ~ 2.0 × length (Fig. 6 B View Figure 6 ). Male pleon large, broadly triangular, pleonite 6 width ~ 2.6 × length; telson width ~ 1.8 × length (Fig. 6 C View Figure 6 ). Female pleon subovate (Fig. 6 E View Figure 6 ). G 1 large, strongly sinuous, tip exceeding suture between thoracic sternites 4 / 5 in situ (Fig. 6 D View Figure 6 ); subterminal segment length ~ 2.3 × length of terminal segment (Fig. 7 C – E View Figure 7 ). Subterminal segment outer margin strongly concave; terminal segment short, rounded, distoventrally with long setae, directed inwards, inner-proximal margin concave; tip presenting as protrusion on higher two-thirds of outer margin (Figs 7 C – E View Figure 7 , 11 A, B View Figure 11 ). G 2 subterminal segment slightly bent outwards distally, flagelliform terminal segment thick, ~ 1.7 × length of subterminal segment, apex blunt, slightly swollen (Fig. 7 B View Figure 7 ).

Description.

Carapace broader than long, ~ 1.2 × as wide as long in males (n = 4), ~ 1.3 × as wide in mature females (n = 4); regions not pronounced, dorsal surface convex; surface finely pitted, anterolateral regions slightly rugose (Fig. 5 View Figure 5 ). Frontal margin slightly sinuous, deflexed (Fig. 5 View Figure 5 ). Epigastric cristae and postorbital cristae rugose, low, almost confluent; bifurcated shallow groove between epigastric cristae (Fig. 5 View Figure 5 ). Branchial regions not swollen (Fig. 5 View Figure 5 ). Cervical groove shallow (Fig. 5 View Figure 5 ). Mesogastric region flat (Fig. 5 View Figure 5 ). External orbital angle broadly triangular, outer margin slightly convex, confluent with anterolateral margin (Figs 5 View Figure 5 , 6 A View Figure 6 ). Epibranchial tooth granular, indistinct (Figs 5 View Figure 5 , 6 A View Figure 6 ). Anterolateral margin lined with 10–14 granules; posterolateral margin posteriorly convergent (Fig. 5 View Figure 5 ); posterolateral surface smooth (Fig. 5 View Figure 5 ). Orbits regular; supraorbital margins weakly cristate, infraorbital margins lined with fused granules (Fig. 6 A View Figure 6 ). Eyes normal (Figs 5 View Figure 5 , 6 A View Figure 6 ). Sub-orbital, pterygostomial and sub-hepatic regions generally smooth, pitted (Fig. 6 A View Figure 6 ). Antennules large, folded within broad fossae; antennae very short (Fig. 6 A View Figure 6 ). Median lobe of epistome buccal margin triangular, lateral margins straight (Fig. 6 A View Figure 6 ).

Maxilliped 3 merus subtrapezoidal, with slight median depression, width ~ 1.2 × length; ischium subtrapezoidal with shallow median sulcus, distomesial margin rounded, width ~ 0.7 × length. Exopod reaching proximal one-third of merus; flagellum absent (Fig. 4 A View Figure 4 ).

Chelipeds (pereiopod 1) subequal (Fig. 7 F – I View Figure 7 ). Merus trigonal in cross section, surfaces generally smooth; outer dorsal margin slightly crenulated, inner and ventral margin lined with large granules (Figs 5 View Figure 5 , 6 A View Figure 6 ). Carpus dorsal surface slightly rugose, with small blunt spine at inner-distal angle, spinule at base (Fig. 5 View Figure 5 ). Major cheliped palm length ~ 1.3–1.4 × height in males (n = 2), 1.4–1.5 × height in females (n = 4); dactylus 0.9 × palm length in males (n = 2), 0.9–1.0 × palm length in females (n = 4) (Fig. 7 F – I View Figure 7 ). Palm surface pitted, occlusal margin of fingers with 8–11 irregular blunt teeth, with very small gape when closed (Fig. 7 F – I View Figure 7 ).

Ambulatory legs slender (pereiopods 2–5) covered with setae, especially dense on pereiopods 2, 3 (Fig. 5 View Figure 5 ). Pereiopod 3 merus 0.6–0.7 × CL in both sexes (n = 8, Fig. 5 View Figure 5 ). Pereiopod 5 propodus length 1.9–2.2 × height in males (n = 4), 2.1–2.4 × height in females (n = 4), shorter than dactylus (Fig. 5 View Figure 5 ).

Male thoracic sternum generally smooth, sparsely pitted; sternites 1–4 width ~ 2.0 × length; sternites 1, 2 fused to form broad triangle; fused sternites 1, 2 demarcated from sternite 3 by almost straight transverse sulcus; sternites 3, 4 fused without obvious demarcation (Fig. 6 B View Figure 6 ). Male sterno-pleonal cavity reaching anteriorly slightly beyond mid-length of cheliped coxa (Fig. 6 B View Figure 6 ). Male pleonal locking tubercle positioned at mid-length of sternite 5 (Fig. 6 D View Figure 6 ). Female vulvae ovate, large, reaching suture of sternites 5 / 6, relatively widely separated (Fig. 6 F View Figure 6 ).

Male pleon large, broadly triangular; somites 3–6 progressively narrower; somite 6 width ~ 2.6 × length; telson width 1.8 × length; lateral margins almost straight, apex rounded (Fig. 6 C View Figure 6 ). Female pleon sub-ovate (Fig. 6 E View Figure 6 ).

G 1 large, strongly sinuous, tip exceeding suture between thoracic sternites 4 / 5 in situ (Fig. 6 D View Figure 6 ); subterminal segment length ~ 2.3 × length of terminal segment (Fig. 7 C – E View Figure 7 ). Subterminal segment outer margin strongly concave; terminal segment short, rounded, distoventral region with long setae, directed inwards, inner-proximal margin concave; tip presenting as protrusion on higher two-thirds of outer margin (Figs 7 C – E View Figure 7 , 11 A, B View Figure 11 ). G 2 subterminal segment slightly bent outwards distally, flagelliform terminal segment thick, ~ 1.7 × length of subterminal segment, apex blunt, slightly swollen (Fig. 7 B View Figure 7 ).

Colour in life.

Generally drab camouflage-brown all over, some individuals exhibit a reddish hue (Fig. 13 B, C View Figure 13 ).

Habitat.

Little is known about the ecology of this new species, aside from its occurrence at high elevations, where it inhabits seepages and is occasionally seen roaming the forest floor. Megapleonum ferrumequinum sp. nov. and Eurusamon guangdongense are also found on the same mountain, but the three species apparently occupy different niches.

Distribution.

Dawuling Nature Reserve, Maoming City, Guangdong Province, China.

Etymology.

This species is named in honour of its discoverer, Jian Wang, in recognition of his contribution to this study.

Remarks.

Like many species in this genus, Megapleonum wangjiani sp. nov. can immediately be distinguished by its distinctive G 1, especially in the rounded terminal segment with the tip presenting as a protrusion on the higher two-thirds of the outer margin (Figs 7 C – E View Figure 7 , 11 A, B View Figure 11 ). Apart from the G 1, M. wangjiani can be separated from the sympatric M. ferrumequinum sp. nov. by its slenderer legs, with the pereiopod 5 propodus length 1.9–2.4 × height, shorter than dactylus, whereas in the latter the pereiopod 5 propodus length is 1.7 × height, longer than dactylus (Fig. 5 A, B View Figure 5 vs Fig. 3 A View Figure 3 ). Megapleonum wangjiani sp. nov. also has a broader male abdomen than M. ferrumequinum n. sp. (Fig. 6 C View Figure 6 vs Fig. 3 D View Figure 3 ). More detailed comparisons can be found in Table 1 View Table 1 .

There is noticeable sexual dimorphism in Megapleonum wangjiani sp. nov., with males being smaller and maturing at a smaller size than females (the male SYSBM 002147 at CW 8.3 mm has a full length G 1 whereas the female SYSBM 002151 at CW 9.3 mm has an immature narrow abdomen). Females also have a proportionally wider carapace (1.2 × as wide as long in mature males vs ~ 1.3 × in mature females) and more slender legs than females (pereiopod 5 propodus length 1.9–2.2 × height in males vs 2.1–2.4 × height in females), but these differences might also be related to size and are only obvious due to the apparent inability for the males to reach the size of females. Interspecific variation of the G 1 is small, with the tip opening varying slightly in size and shape (Fig. 7 C – E View Figure 7 ).